1. Field of the Invention
This invention relates to a method of steering a mining machine cutter in which the mining machine is of the kind having a body arranged to the progressed along a mineral face being cut, the body having at either end a ranging arm pivotally mounted on the body and each arm carrying a rotatable cutting drum. This kind of machine is known as a double-ended ranging drum shearer.
2. Prior Art
Such a machine carries a plurality of sensor means mounted on the machine which are adapted to measure different parameters of the mining operation and to generate electrical signals representative of said parameters. For example, a first of said sensor means may be arranged to measure along the face angle or tilt of the machine, second sensor means may be arranged to measure the movement and direction of the machine and a third of said sensor means may be arranged to measure the positions of the leading and trailing ranging arms with respect to the machine. The invention also encompasses apparatus for use with the method.
In mineral cutting operations, particularly those concerning coal, it is necessary to steer a cutting machine to enable the maximum efficiency of operation to be achieved by ensuring that only the desired mineral, i.e. coal, is cut and the machine does not wander into strata on either side of the coal. In order to do this, it is normal to leave a few inches of the material being cut to form a roof and floor so that any minor variations in the path of the cutting machine only varies the thickness of the roof and floor left and does not cut into the adjoining strata.
Many means of cutting and extracting wanted mineral are known, but the most commonly used form, particularly for winning coal, is to use a ranging drum machine having ranging arms at either end where a cutting drum having a plurality of cutting picks is rotated at the end of each ranging arm which is pivotally secured to the body of a machine. The body of the machine is pulled along a face and each rotating drum cuts material from the face.
This type of machine is steered to enable the drum always to cut within the seam by adjusting the pivotal control of the ranging arms. This can be done manually by skilled operators who watch the progress of the drum and the seam, but generally automatic means are preferred since the creation of dust and water sprays can impair the vision of the drum by the operators.
Automatic sensing of the roof has been proposed and is operated in a large number of installations. In one form of automatic sensing a sensor device is carried on the machine and this measures gamma rays emitted from the roof of the seam being cut and a count of these rays attenuated by the amount of wanted material remaining on the roof is picked up by the sensor device on the machine and this produces a control signal which is inversely proportional to roof coal thickness. This control signal can be used with other signals to control the angle at which the ranging arm is set so as to ensure a substantially constant thickness of material left on the roof. A second sensor device can be mounted in a roof following position on the ranging arm of the machine physically to engage the roof which has previously been cut. This sensor device produces a signal to determine the height of the cutting drum with respect to the previously exposed roof. A third sensor device can be incorporated to measure the angle of the machine in face advance. This device produces a signal related to the said angle and is used to give stability to the system.
At present double-ended ranging drum shearers use the sensor devices to control the shearer so that the leading drum leaves the desired thickness of wanted material (coal) on the roof and the trailing drum, which is offset from the roof, cuts a constant extraction. Since there is a requirement to position the trailing drum some distance from the roof, the roof follower arms previously used have all been of a relatively long nature and the end of the arm, carrying a wear area which abuts the roof, is located behind the drum so that it is giving instructions to the steering control to follow as closely as possible the passage of the drum. Unfortunately the long roof follower arm is prone to damage producing erroneous reading. The use of a shorter follower arm has previously been proposed in our previous Patent Specification No. 2 121 852 where a small pivoted follower arm is located on the ranging arm itself in the vicinity of the cutting drum.